RF Amplifier Package with Biasing Strip

ABSTRACT

Embodiments of an RF amplifier package include a body section comprising an upper surface having first and second opposing edge sides, and a die pad vertically recessed beneath the upper surface and comprising first and second opposing sides and a third side intersecting with the first and second sides. Embodiments also include first and second leads disposed on the upper surface, the second lead extending from adjacent to the second side to the second edge side; and a biasing strip connected to the second lead and disposed on the upper surface adjacent to the third side. Other embodiments include packaged RF amplifiers comprising an RF amplifier package, and an RF transistor mounted on the die pad and comprising: a control terminal electrically coupled to the first lead, a reference potential terminal directly facing and electrically connected to the die pad, and an output terminal electrically connected to the second lead.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of, and claims the benefit ofpriority from, U.S. patent application Ser. No. 15/709,532 filed on Sep.20, 2017, the entire disclosure of which is incorporated herein byreference for all purposes

FIELD OF TECHNOLOGY

The present application relates to RF (radio frequency) amplifiers, andin particular relates to package designs for RF amplifiers.

BACKGROUND

RF power amplifiers are used in a variety of applications such as basestations for wireless communication systems, etc. The signals amplifiedby the RF power amplifiers often include signals that have a highfrequency modulated carrier having frequencies in the 400 megahertz(MHz) to 60 gigahertz (GHz) range. The baseband signal that modulatesthe carrier is typically at a relatively lower frequency and, dependingon the application, can be up to 300 MHz or higher. Many RF poweramplifier designs utilize a semiconductor switching device as theamplification device. Examples of these switching devices include powertransistor devices, such as a MOSFET (metal-oxide semiconductorfield-effect transistor), a DMOS (double-diffused metal-oxidesemiconductor) transistor, a GaN HEMT (gallium nitride high electronmobility transistor), a GaN MESFET (gallium nitride metal-semiconductorfield-effect transistor), an LDMOS transistor, etc.

A device package for an RF power amplifier can include a transistor die(e.g., MOSFET (metal-oxide semiconductor field-effect transistor), LDMOS(laterally-diffused metal-oxide semiconductor), HEMT (high electronmobility transistor) along with an input and output impedance matchingcircuit incorporated therein. The input and output impedance matchingcircuits typically include LC networks that provide at least a portionof an impedance matching circuit that is configured to match theimpedance of the transistor die to a fixed value.

Class F amplifier configurations are gaining increased favor due totheir highly efficient operation in modern RF applications. Class Famplifier design requires careful tuning of higher order harmonics.Power efficiency can be improved by incorporating harmonic tuningcircuits in to the input and output impedance matching circuits that areincorporated into the device package.

Modern RF power amplifiers are required to maintain as high efficiencyas possible over a high range of output power. This design imperativecan be particularly challenging in RF power amplifiers with smalldevices or devices with high power density (e.g., GaN HEMT devices).These devices are typically packaged with a number of electricallyconductive bond wires connected between the input and output terminalsof the transistor die and the package leads. In this configuration,capacitive coupling can occur between the various wires of the packageddevice and/or between the bond wires and the substrate portion of thepackage. Currently, GaN HEMT devices are predominantly “bonded straightout.” This means that the drain of the transistor die is directlyelectrically connected to a lead of the package by a set of dedicatedbond wires. This package configuration is easy to produce in practice,but results in a large parasitic network at the output of thetransistor. This parasitic network limits the ability to tune higherorder harmonics. This parasitic network is also detrimental for thebaseband impedance (i.e., the impedance presented in the fundamentaloperating frequency range), a metric which is important for thelinearizability of the transistor. The bond wires in conjunction withthe package effectively appear as an inductance, which forms a resonatorin parallel with the parasitic output impedance of the transistor. Thispresents a high impedance to the transistor which in turn generates alarge gain spike in the baseband region.

SUMMARY

An RF semiconductor amplifier package is disclosed. According to anembodiment, the RF semiconductor amplifier package includes a flangeshaped body section, an electrically conductive die pad centrallylocated on the body section, and an electrically insulating window framedisposed on an upper surface of the body section and surrounding the diepad. The RF semiconductor amplifier package further includes a firstelectrically conductive lead disposed on the window frame adjacent to afirst side of the die pad and extending away from the first side of thedie pad towards a first edge side of the body section. The RFsemiconductor amplifier package further includes a second electricallyconductive lead disposed on the window frame adjacent to a second sideof the die pad and extending away from the second side of the die padtowards a second edge side of the body section, the second side of thedie pad being opposite the first side of the die pad. The RFsemiconductor amplifier package further includes a first electricallyconductive biasing strip that is disposed on the window frame,continuously connected to the second lead, and extends along and a thirdside of the die pad. The third side of the die pad extends between thefirst and second sides of the die pad.

According to another embodiment, the RF semiconductor amplifier packageincludes a flange shaped body section having a first edge side and asecond edge side opposite the first edge side, an electricallyconductive die pad centrally located on the body section between thefirst and second edge sides, an electrically insulating window framedisposed on an upper surface of the section and surrounding the die pad,and a continuous electrically conductive structure disposed on thewindow frame and electrically insulated from the die pad. The continuouselectrically conductive structure includes a lead portion extending awayfrom the die pad towards the second edge side of the body section, and abiasing strip that extends around an outer perimeter of the die padtowards the first edge side of the body section.

A packaged RF amplifier is disclosed. According to an embodiment, thepackaged RF amplifier includes an RF package, including: a flange shapedbody section, an electrically conductive die pad, an electricallyconductive input lead that is insulated from the die pad and extendsaway from a first edge side of the die pad, an electrically conductiveoutput lead that is insulated from the die pad and extends away from asecond edge side of the die pad in an opposite direction as the inputlead, and a first electrically conductive biasing strip that iscontinuously connected to the electrically conductive output lead andextends around an outer perimeter of the die pad towards the first edgeside of the flange. The packaged RF amplifier further includes an RFtransistor mounted on the die pad. The RF transistor includes: a controlterminal that is electrically coupled to the first lead, a referencepotential terminal that directly faces and is electrically connected tothe die pad, and an output terminal that is electrically connected tothe second lead.

BRIEF DESCRIPTION OF THE DRAWINGS

The elements of the drawings are not necessarily to scale relative toeach other. Like reference numerals designate corresponding similarparts. The features of the various illustrated embodiments can becombined unless they exclude each other. Embodiments are depicted in thedrawings and are detailed in the description which follows.

FIG. 1 depicts an RF amplifier package with a biasing strip, accordingto an embodiment.

FIG. 2, which includes FIGS. 2A and 2B, depicts a packaged RF amplifierwith a biasing strip, according to an embodiment. FIG. 2A depicts a planview of the packaged RF amplifier, and FIG. 2B depicts an isometric viewof the packaged RF amplifier.

FIG. 3 depicts an equivalent electrical schematic of the packaged RFamplifier of FIG. 2, according to an embodiment.

FIG. 4, which includes FIGS. 4A and 4B, depicts a packaged RF amplifier,according to another embodiment. FIG. 4A depicts an equivalent schematicof the packaged RF amplifier, and FIG. 4B depicts a close-up view of thepackage portion that includes decoupling capacitors.

FIG. 5, which includes FIGS. 5A and 5B, depicts a packaged RF amplifier,according to another embodiment. FIG. 5A depicts an equivalent schematicof the packaged RF amplifier, and FIG. 5B depicts a plan view of thepackage and capacitors that are mounted outside of the package.

FIG. 6, which includes FIGS. 6A, 6B and 6C, depicts a packaged RFamplifier, according to another embodiment. FIG. 6A depicts anequivalent schematic of the packaged RF amplifier, FIG. 6B depicts aclose-up view of the package portion that includes a radial stub, andFIG. 6C depicts a close-up view of the package portion that includes asurface mount technology capacitor.

DETAILED DESCRIPTION

According to embodiments described herein, an RF amplifier package isdisclosed. The package includes a metal flange, an electricallyconductive die pad centrally located on the metal flange, and anelectrically insulating window frame disposed on an upper surface of themetal flange and surrounding the die pad. Electrically conductive inputand output leads are leads are disposed on the window frame and extendaway from either side of die pad. Integrated circuit components, e.g.,transistors, capacitors, etc., can be mounted on the die pad andelectrically connected to the input and output leads using bond wires,for example.

Advantageously, the RF amplifier package includes an electricallyconductive biasing strip that extends along a side of the die pad thatis not adjacent to any package leads. According to one embodiment, thebiasing strip is continuously connected to the output lead of the RFamplifier package. The biasing strip can advantageously be isolated fromthe RF signal that is transmitted on the output lead. By providing theelectrically conductive biasing strip in the RF amplifier package, asubstantially greater area is made available for the electricalconnection of components in the output network of the amplifier device.This produces numerous benefits, some of which will be discussed in thefollowing description of the figures.

Referring to FIG. 1, an RF amplifier package 100 is depicted, accordingto an embodiment. The RF amplifier package 100 includes a flange shapedbody section 102. The flange shaped body section 102 is configured to beinserted into an external apparatus, such as the socket of a printedcircuit board, and is configured to provide a conduit between theexternal apparatus and one or more integrated circuits that are mountedon the flange portion. In some embodiments, the flange shaped bodysection 102 is configured as a heat sink that dissipates heat away fromthe integrated circuits mounted thereon to an external heat sink.Generally speaking, the body section 102 can include electricallyconductive materials, and/or thermally conductive materials,electrically insulating materials, and/or thermally insulatingmaterials. Exemplary insulating materials (both thermal and electrical)include ceramics, plastics, and semiconductor based insulators such assemiconductor oxides, semiconductor nitrides and semiconductoroxynitrides. Exemplary conductive materials include metals such ascopper, aluminum and alloys thereof.

The RF amplifier package 100 additionally includes an electricallyconductive die pad 104 centrally located on the body section 102. Asused herein, “centrally located” refers to the fact that the die pad 104is completely laterally spaced apart from every outer edge side of thebody section 102. The die pad 104 can have a generally planar uppersurface that is configured to accommodate one or more integrated circuitdevices (e.g., transistors, chip capacitors, etc.) directly mountedthereon. In one embodiment, the upper surface of the die pad 104 isvertically recessed on a plane that is beneath an upper surface 106 ofthe body section 102. That is, a ridge is formed in the body section 102around the perimeter of the die pad 104. The die pad 104 can have avariety of different geometries. In the depicted embodiment, the die pad104 has a square geometry. Other rectangular geometries are possible.More generally, the die pad 104 can have the geometry of any enclosedshape.

The die pad 104 can include any of a variety of electrically conductivematerials, including electrically conductive metals such as copper,aluminum and alloys thereof. In one embodiment, the die pad 104 is partof a metal baseplate that is made of an electrically and thermallyconductive material such as Cu, CPC (copper, copper-molybendum, copperlaminate structure), CuW, etc. A metal slug (not shown) can be disposedbeneath the baseplate, and a heatsink (not shown) including a thermalconductor, e.g., aluminum or copper can be disposed beneath the metalslug and extend to a lower side of the RF semiconductor amplifier. Inthis way, the semiconductor amplifier package acts as a heat sink. Anexample of such a structure is disclosed in U.S. Pat. No. 9,629,246 toMu, the content of which is incorporated by reference in its entirety.

The RF amplifier package 100 additionally includes an electricallyinsulating window frame 108 that is disposed on the upper surface 106 ofthe of the body section 102. The electrically insulating window frame108 can include a variety of electrically and/or thermally insulatingmaterials such as ceramic, plastic, etc. The electrically insulatingwindow frame 108 surrounds the die pad 104. That is, the electricallyinsulating window frame 108 forms an enclosed loop around the peripheryof the die pad 104. Optionally, as shown in the figures, theelectrically insulating window frame 108 can completely cover all of theexposed upper surface 106 of the body section 102 outside of the die pad104.

The RF amplifier package 100 further includes a plurality ofelectrically conductive leads. The electrically conductive leads can beformed from any of a variety of electrically conductive materials,including electrically conductive metals such as copper, aluminum andalloys thereof. The leads provide electrical access between the packagedcomponents that are mounted on the die pad 104 and an externalapparatus, e.g., a printed circuit board. At a minimum, the RF amplifierpackage 100 includes at least two leads. In the depicted embodiment, thepackage includes a first lead 110 and a second lead 112. The first andsecond leads 110, 112, may be, but are not necessarily, substantiallyequal in width. Generally speaking, the first and second leads 110, 112may have a variety of different shapes and sizes different from thoseshapes that are depicted in FIG. 1.

Both the first and second leads 110, 112 are disposed on the windowframe 108 adjacent to the die pad 104. The first lead 110 extends awayfrom a first side 114 of the die pad 104 towards a first edge side 116(identified in FIG. 2A) of the body section 102. On an opposite side ofthe RF amplifier package 100, the second lead 112 extends away from asecond side 118 (identified in FIG. 2A) of the die pad 104 towards atowards a second edge side 120 of the body section 102 that is oppositeform the first edge side 116 of the body section 102. Thus, the firstand second leads 110, 112 extend away from one another in oppositedirections. In the depicted embodiment, the first lead 110 terminates atthe first edge side 116 of the body section 102 and the second lead 112terminates at the second edge side 120 of the body section 102. That is,outer edge sides of the first and second leads 110, 112 are coextensivewith the outer edges of the body section 102. In other embodiments, thefirst and second leads 110, 112 may extend past the first and secondedge sides 116, 120 of the body section 102, respectively.

According to one embodiment, the RF amplifier package 100 is a so-calledPCB based RF-power package. Examples of these package designs aredescribed in U.S. Pat. No. 8,907,467 to Komposch, the content of whichis incorporated by reference in its entirety, and U.S. PG PUB2017/0245359 to Mu, the content of which is incorporated by reference inits entirety. To summarize the design of these package types, thepackage design is treated as part of the electrical design of the systeminstead of a just a mechanical component. To this end, the RF amplifierpackage 100 can include a multilayer printed circuit board that isincorporated into the body section 102. This multilayer printed circuitboard includes signal and ground layers. Various RF components can beembedded within the multi-layer circuit board using the embedded signallayer. Examples of these RF components include integrated harmonicsresonators, balanced power combiner networks, etc. In this way, fewerexternal components are needed and space efficiency of the package isimproved.

The RF amplifier package 100 additionally includes a first electricallyconductive biasing strip 122. The first biasing strip 122 can becontinuously connected to the second lead 112. That is, the second lead112 and the first biasing strip 122 can collectively form anuninterrupted path of electrically conductive material. For example, thefirst biasing strip 122 and the second lead 112 can be part of a commonmetal later that is patterned and affixed or disposed on top of thewindow frame 108, or integrated within the body section 102 as part of aPCB structure. The first biasing strip 122 is disposed on the windowframe 108 adjacent to the die pad 104. According to an embodiment, thefirst biasing strip 122 is immediately adjacent to the die pad 104. Insome embodiments, the first biasing strip 122 can be situated as closeto the die pad 104 as is practically possible within processingcapabilities.

Advantageously, the first biasing strip 122 provides additional lateralspace for the electrical connection of elements that are disposed on thedie pad 104 to an external bias. FIG. 1 illustrates one potentialconfiguration of integrated circuit elements that advantageouslyutilizes the additional connection area provided by the first biasingstrip 122. In the depicted embodiment, a first integrated circuit 124 isdisposed on the die pad 104 immediately adjacent to the second side 118of the die pad 104. This first integrated circuit 124 may be an RFtransistor, for example. A direct electrical connection between thefirst integrated circuit 124 and the second lead 112 is effectuated by afirst set 126 of electrically conductive bond wires that are directlyconnected between the first integrated circuit 124 element and thesecond lead 112. Meanwhile, a second integrated circuit 128 is disposedon the die pad 104 immediately adjacent to a third side 130 of the diepad 104. The third side 130 of the die pad 104 extends between the firstand second sides 114, 118 of the die pad 104, and is immediatelyadjacent to the first biasing strip 122. A direct electrical connectionbetween the second integrated circuit 128 and the first biasing strip122 is effectuated by a second set 132 of electrically conductive bondwires that are directly connected between the second integrated circuit128 and the first biasing strip 122.

The provision of the first biasing strip 122 in the RF amplifier package100 advantageously improves the space efficiency and electricalperformance of the RF amplifier package 100 in comparison toconventional designs. In a conventional package design that does notinclude the first biasing strip 122, the elements of the outputimpedance matching network (e.g., chip capacitors) should ideally beplaced as close as possible to the output terminal of the RF transistorfor minimal degradation in performance due to parasitic effects. Thepresence of these elements near the output terminal of the RF transistorrestricts the number of bond wires that can connect the transistor dieto the output lead, as these bond wires from the various elements areinterleaved with one another. Moreover, this configuration is prone tointerference due to the close proximity of the various bond wires. Incomparison, the configuration shown in FIG. 1 allows the outputcapacitors to be moved to a different location of the die pad 104 withthe transistor die being disposed immediately adjacent to the outputlead. A greater number of bond wires can be used to directly connect thetransistor die to the output lead (i.e., the second lead 112 in thedepicted arrangement). Moreover, these bond wires are substantiallyspaced apart from the bond wires that connect capacitors in the outputmatching network such that interference between the two is non-existentor negligible.

The first biasing strip 122 is formed to extend around the perimeter ofthe die pad 104 in such a way that it extends towards the first edgeside 116 of the body section 102. Thus, the first biasing strip 122includes a portion that extends in an opposite direction as the secondlead 112. In the depicted embodiment, the die pad 104 is rectangular,and has linear third and fourth sides 130, 134 that each form aperpendicular angle with the linear first and second sides 114, 118. Thefirst biasing strip 122 extends away from the second lead 112 and aroundthe perpendicular corner formed between the second and third sides 118,130 of the die pad 104 so as to travel alongside and parallel to thethird side 130 of the die pad 104. To this end, the first biasing strip122 includes a first section 136 that is connected to the second lead112 and extends along a portion of the second side 118 of the die pad104 and around the corner between the second and third sides of the diepad 104. At this location, the first section 136 forms a perpendicularintersection with a second elongated section 138 of the first biasingstrip 122. This intersection between the second elongated section 138and the first section 136 of the first biasing strip 122 is immediatelyadjacent to the corner between the second and third sides 118, 132 ofthe die pad 104. The second elongated section 138 of the first biasingstrip 122 extends at least partially along the third side 130 of the diepad 104 while being disposed immediately adjacent to the third side 130of the die pad 104. According to one embodiment, the second elongatedsection 138 extends completely along the third side 130 of the die pad104. That is, the second elongated section 138 of the first biasingstrip 122 extends at least to the first side 114 of the die pad 104.Optionally, the second elongated section 138 of the first biasing strip122 may extend completely and continuously across the body section 102so as to reach the first edge side 116 of the body section 102. Thisfeature is shown in FIG. 2. In addition, an enlarged pad portion 140 maybe provided at the end of the second elongated section 138 of the firstbiasing strip 122 so as to provide increased area for externalconnections, e.g., from external bond wires or conductive traces. Thisfeature is also shown in FIG. 2.

Referring again to FIG. 1, the RF amplifier package 100 may optionallyinclude a second biasing strip 142 that is configured to provideadditional lateral space for the electrical connection of elements thatare disposed on the die pad 104 to an external bias in a similar manneras previously described with reference to the first biasing strip 122.The second biasing strip 142 includes a third section 144 that extendsalong the second side 118 of the die pad 104 and a fourth elongatedsection 146 that forms an angled intersection with the third section144. The fourth elongated section 146 is immediately adjacent to thefourth side 134 of the die pad 104 that extends between the first andsecond sides, and is opposite to the third side 130 of the die pad 104.In the depicted embodiment, the fourth elongated section 146 extendscompletely along the fourth side 134 of the die pad 104, but does notreach the first edge side 116 of the body section 102. In otherembodiments, the fourth elongated section 146 may extend further toreach the first edge side 116 of the body section 102. As shown in FIG.1, a third integrated circuit 148 may be electrically connected to thesecond biasing strip 142 in a similar manner as previously describedwith respect to the first biasing strip 122.

Depending on the geometry of the die pad 104, the geometry of the firstbiasing strip 122 and/or the second biasing strip 142 may becorrespondingly adapted to at least partially extend around a perimeterof the die pad 104 to reach a location that is sufficiently distant tothe second lead 112 to provide a connection location for multiplediscrete components, e.g., as depicted in FIG. 1. Although the depictedembodiment shows a rectangular shaped die pad 104, a variety ofdifferent die pad 104 geometries are possible. For example, the outerperimeter of the die pad 104 may include an angled intersection betweentwo linear sides that form an oblique angle with one another. In thiscase, the first biasing strip 122 and/or the second biasing strip 142may include two linear sections that form a corresponding oblique anglewith one another that is adjacent to the oblique angle in the outerperimeter of the die pad 104. Similarly, the outer perimeter of the diepad 104 may include one or more curves and the sections of the firstbiasing strip 122 and/or the second biasing strip 142 can be formed withcorresponding curves that mirror this geometry.

Referring to FIG. 2, a packaged RF amplifier 200 is depicted, accordingto an embodiment. The packaged RF amplifier 200 includes the RFamplifier package 100 as described with reference to FIG. 1. In thisconfiguration, the first lead 110 provides an input lead for thepackaged RF amplifier 200 and the second lead 112 provides an outputlead for the packaged RF amplifier 200. An RF transistor 202 is mountedon the die pad 104. The RF transistor 202 is mounted immediatelyadjacent to the second side 118 of the die pad 104. Accordingly, thereare no other discrete elements disposed between the RF transistor 202and the second side 118 of the die pad 104.

The RF transistor 202 can be selected form a variety of different devicetypes, such as LDMOS (laterally diffused metal-oxide-semiconductor),IGBT (insulated gate bipolar transistor), HEMT (high electron mobilityelectron transistor), etc. These device types can be formed in a varietyof different semiconductor material technologies, e.g., Si (silicon),SiC (silicon carbide), SiGe (silicon germanium), GaN (gallium nitride),GaAs (gallium arsenide), etc. In the depicted embodiment, the RFtransistor 202 die has a so-called “source down” configuration. In thisconfiguration, the lower surface of the RF transistor 202 includes anelectrically conductive source terminal that faces and directlyelectrically connects with the die pad 104. Attachment and electricalconnection between the source terminal and the die pad 104 can beprovided by a conductive paste or solder. In this configuration, the diepad 104 acts as an electrical terminal of the package (e.g., a GNDterminal) as well as a mounting surface for the RF transistor 202. Acontrol terminal of the RF transistor 202 (e.g., a gate terminal) and anoutput terminal of the of the RF transistor 202 (e.g., a drain terminal)are disposed on an upper surface of the RF transistor 202 die that isopposite the lower surface of the RF transistor 202.

The control terminal of the RF transistor 202 is electrically coupled tothe first lead 110. In the depicted embodiment, this electrical couplingis provided by an input group 204 of bond wires that is electricallyconnected between the control terminal of the RF transistor 202 and thefirst lead 110. Optionally, the packaged RF amplifier 200 may includefirst and second input capacitors 206, 208 that are disposed between theRF transistor 202 and the first lead 110. These first and second inputcapacitors 206, 208 include lower terminals that directly face andelectrically connect to the die pad 104 and upper terminals that faceaway from the die pad 104. The input group 204 of bond wires of bondwires forms a series electrical connection between the first lead 110,the upper terminals of the first and second input capacitors 206, 208,and the control terminal of the RF transistor 202.

The output terminal of the RF transistor 202 is electrically coupled tothe second lead 112. According to an embodiment, this electricalcoupling is provided by a first set of 210 electrically conductive bondwires that extends directly from the output terminal of the RFtransistor 202 to the second lead 112.

The packaged RF amplifier 200 further includes a first capacitor 212that is mounted on the die pad 104. The first capacitor 212 is mountedimmediately adjacent to the third side 130 of the die pad 104. That is,there are no other discrete elements disposed between the firstcapacitor 212 and the third side 130 of the die pad 104. The firstcapacitor 212 is configured as a chip capacitor with a lower terminalthat directly faces and electrically connects to the die pad 104. Anupper terminal of the first capacitor 212 faces away from the die pad104. The upper terminal of the first capacitor 212 is electricallyconnected to the first biasing strip 122. According to an embodiment,this electrical coupling is provided by a second set 214 of electricallyconductive bond wires that extends directly from the upper terminal ofthe first capacitor 212 to the first biasing strip 122.

Optionally, the packaged RF amplifier 200 further includes a secondcapacitor 216 that is mounted on the die pad 104. The second capacitor216 is mounted immediately adjacent to the fourth side 134 of the diepad 104. That is, there are no other discrete elements disposed betweenthe RF transistor 202 and the fourth side 134 of the die pad 104. Thesecond capacitor 216 is configured as a chip capacitor with a lowerterminal that directly faces and electrically connects to the die pad104. An upper terminal of the second capacitor 216 faces away from thedie pad 104. The upper terminal of the first capacitor 212 iselectrically connected to the second biasing strip 142. According to anembodiment, this electrical coupling is provided by a third 218 set ofelectrically conductive bond wires that extends directly from the upperterminal of the second capacitor 216 to the second biasing strip 142.

Referring to FIG. 3, a circuit schematic of an amplifier circuit 300that includes the packaged RF amplifier 200 described with reference toFIG. 2 is depicted. A package outline 302 provided in the schematic todelineates the circuit elements that are provided within the packaged RFamplifier 200 from the circuit elements that are provided outside of thepackaged RF amplifier 200.

The amplifier circuit 300 includes an input impedance matching network304 connected between the input terminal of the packaged RF amplifier200 and the control terminal of the RF transistor 202. The inputimpedance matching network 304 is provided by the input group 204 ofbond wires and the first and second input capacitors 206, 208. The inputgroup 204 of bond wires act as inductors in this network, and the heightand spacing of the input group 204 of bond wires can be adjusted toprovide a desired inductance. This input impedance matching network 304can be configured to, among other things, match an input impedance ofthe amplifier circuit 300 to a fixed value, e.g., 50 ohms.

The amplifier circuit 300 additionally includes an output impedancematching network 306 connected between the output terminal of the RFtransistor 202 and the output terminal of the packaged RF amplifier 200.The output impedance matching network 306 includes a first LC resonator308 that is connected in parallel with the output of the RF transistor202. The capacitance of the first LC resonator 308 is provided at leastin part by the first capacitor 212. The inductance of the of the firstLC resonator 308 is provided by the combination of the second set 214 ofbond wires and the first biasing strip 122. Additional capacitance andinductance can be added using the second biasing strip 142 and thesecond capacitor 216. In either case, the inductance of the first LCresonator 308 can be can be adjusted by appropriately tailoring thephysical parameters of the second biasing strip 142 (e.g., width, shape,etc.). The first LC resonator 308 is configured form a parallel resonantcircuit with the characteristic output capacitance of the RF transistor202 and thereby improve the output efficiency of the circuit.

Outside of the packaged RF amplifier 200, the amplifier circuit 300includes a resistive load 310 that is connected to the second lead 112of the RF amplifier package 100. Additionally, outside of the packagedRF amplifier 200, the amplifier circuit 300 includes a DC decouplingcapacitor 312 that is connected to the output terminal of the RFtransistor 202. The DC decoupling capacitor 312 can be provided in anexternal apparatus, such as a PCB, near the first edge side 116 of thebody section 102. The electrical connection between the output terminalof the RF transistor 202 and the DC decoupling capacitor 312 can beprovided using the first biasing strip 122. In particular, the DCdecoupling capacitor 312 can be connected to the enlarged pad portion140 of the biasing strip that is adjacent the first edge side 116 of thebody section 102, e.g., as described with reference to FIG. 2. The DCdecoupling capacitor 312 has a very large capacitance value (e.g., 1 μF(microfarad) or greater). The DC decoupling capacitor 312 enhancesbaseband performance by maintaining a low impedance at the transistordrain terminal 202.

The design of the RF amplifier package 100 enables several notableperformance benefits for the amplifier circuit 300 in comparison tosimilar RF amplifier circuit topologies that utilize conventionalpackage designs. For example, the parameters of the first LC resonator308 (e.g., inductance and capacitance) have greater flexibility andtunability than conventional package designs. One reason for this isthat the first and second capacitors 212, 216 can be provided usingsilicon capacitors. By way of comparison, MLCC (ceramic surface mountcapacitors) are commonly utilized in conventional straight bondedconfigurations due to space constraints. These space constraints areeliminated by the first biasing strip 122. In addition, because thefirst LC resonator 308 can be formed using PCB materials from thepackage structure (e.g., in an embodiment in which the RF amplifierpackage 100 is configured as a so-called PCB based RF-power package) ahigher quality factor than conventional bond wires is achieved for theinductance portion of the first LC resonator 308.

Referring to FIG. 4, an amplifier circuit 400 is depicted, according toanother embodiment. The amplifier circuit 400 is substantially identicalto the amplifier circuit 300 described with reference to FIG. 3 with theexception that the DC decoupling capacitor 312 is mounted within the RFamplifier package 100 in the embodiment of FIG. 4. FIG. 4A shows aclose-up view of the RF amplifier package 100 showing a potentialmounting location for the DC decoupling capacitor 312. FIG. 4B shows anequivalent circuit schematic of the amplifier circuit 400.

In this embodiment, the DC decoupling capacitor 312 is mounted on aportion of the body section 102 that is outside of the die pad 104. Thisportion of the body section 102 can include openings in the window frame108 enable a direct electrical connection between a lower terminal ofthe DC decoupling capacitor 312 and the PCB metallization layers thatare provided within the body section 102. In this way, an electricalconnection between the lower terminal of the DC decoupling capacitor 312and the reference potential terminal of the RF amplifier package 100 canbe effectuated. An upper terminal of the DC decoupling capacitor 312 iselectrically connected to the first biasing strip 122 using anelectrically conductive medium, for example bond wires, solder orconductive epoxy. Alternatively, any electrical connection mechanismsuch as bond wires may be used to effectuate this electrical connection.

The arrangement of FIG. 4 advantageously places the DC decouplingcapacitor 312 very close to the output terminal of the RF transistor 202in comparison to a conventional straight bonded design. Thisadvantageously improves baseband performance by minimizing the parasiticinductance between the output terminal of the RF transistor 202 and theDC decoupling capacitor 312.

Referring to FIG. 5, an amplifier circuit 500 is depicted, according toanother embodiment. The amplifier circuit 500 can be substantiallyidentical to the amplifier circuit 300 described with reference to FIG.3 with the exception that both the DC decoupling capacitor 312 and thefirst capacitor 212 that is used for the first LC resonator 308 isprovided outside of the RF amplifier package 100. Both of thesecapacitors 308, 212 can be provided in an external apparatus such as aPCB near the first edge side 116 of the body section 102 andelectrically connected to the first biasing strip 122 using, e.g., theenlarged pad portion 140 of the biasing strip as described withreference to FIG. 2.

The configuration of FIG. 5 may be particularly advantageous in lowfrequency applications (e.g., RF frequencies below 1 GHZ) in which thelarge inductances required to implement the LC shunt match circuit wouldotherwise require long bond wires, which have poor mechanical stabilityand tend to overheat. The configuration of FIG. 5 advantageously allowsfor the inductance of the LC shunt match to be predominatelyattributable to the first biasing strip 122 which can be part of a PCBstructure and is thus more easily tailored than equivalent bond wires.

Referring to FIG. 6, an amplifier circuit 600 is depicted, according toanother embodiment. The amplifier circuit 600 can be substantiallyidentical to the amplifier circuit 300 described with reference to FIG.3 with the exception that a second LC resonator 602 is connected to theoutput terminal of the RF transistor 202. The second LC resonator 602 isprovided within the RF amplifier package 100.

FIG. 6A depicts an equivalent circuit schematic of the amplifier circuit600. In this example, the output impedance matching network 306 isconfigured as a so called “harmonic shunt match.” In this configuration,the first LC resonator 308 forms a parallel resonant circuit with thecharacteristic output impedance of the RF transistor 202 in the mannerpreviously described. In some cases, this shunt match topology tends topresent low impedance to higher order harmonics of the RF signal, whichis undesirable for class F operation. Class F amplifier amplifiersrequire high impedance at the higher order harmonics (e.g., the secondand third harmonics). By splitting the shunt match inductor in two andplacing a small capacitance in the middle, Class F harmonic matching canbe achieved by adding only one additional component to the circuit. Theschematic of FIG. 6A depicts one implementation of this concept in whicha second LC resonator 602 is provided by adding one additionalcomponent. The second LC resonator 602 resonates at one of the higherorder harmonics (e.g., the second harmonic). This concept can be used toform multiple LC resonators that are each tuned to one of the higherorder harmonics (e.g., the second harmonic and the third harmonic,etc.).

FIG. 6B depicts a close-up view of the RF amplifier package 100 showinga potential implementation of the amplifier circuit 600 of FIG. 6A,according to an embodiment. In this embodiment, the second LC resonator602 is provided by incorporating a radial stub 604 in the RF amplifierpackage 100. A “radial stub” as used herein refers to a microstriplinefeature in which the transmission line gradually expands and has acurved outer edge at the widest portion of the transmission line. Thephysical geometry of the radial stub 604 can be tailored to provide adesired RF impedance response, including that of a capacitor at a givenfrequency. The radial stub 104 is provided in a portion of the bodysection 102 that is outside of the die pad 104, and connects to thefirst biasing strip 122 at a location that is between the outputterminal of the RF transistor 202 and the first capacitor 212.

FIG. 6C depicts shows a close-up view of the RF amplifier package 100showing a potential implementation of the amplifier circuit 600 of FIG.6A, according to another embodiment. In this embodiment, the second LCresonator 602 is provided by a discrete SMT (surface mount technology)capacitor 606 that is mounted on a portion of the body section 102 thatis outside of the die pad 104. The SMT capacitor is electricallyconnected to first biasing strip 122 at a location that is between theoutput terminal of the RF transistor 202 and the first capacitor 212.

The term “immediately adjacent” as used herein describes a proximitybetween two elements in which no other intentionally formed features aredisposed between the immediately adjacent elements. For example,embodiments described herein refer to a second elongated section 138 ofthe first biasing strip 122 that is immediately adjacent to the thirdside 130 of the die pad 104. This means that there are no otherintentionally formed structures (e.g., discrete elements, metallizationpads, etc.) disposed between the second elongated section 138 and thethird side 130 of the die pad 104. The second elongated section 138 ofthe first biasing strip 122 may be spaced apart from the third side 130of the die pad 104 with only vacant portions of the body section 102between the two elements and be “immediately adjacent” to the third side130 of the die pad 104.

The term “electrically connected” as used herein describes a permanentlow-ohmic, i.e., low-resistance, connection between electricallyconnected elements, for example a wire connection between the concernedelements. By contrast, the term “electrically coupled” contemplates aconnection in which there is not necessarily a low-resistance connectionand/or not necessarily a permanent connection between the coupledelements. For instance, active elements, such as transistors, as well aspassive elements, such as inductors, capacitors, diodes, resistors,etc., may electrically couple two elements together.

Terms such as “same,” “match,” and “matches” as used herein are intendedto mean identical, nearly identical or approximately so that somereasonable amount of variation is contemplated without departing fromthe spirit of the invention. The term “constant” means not changing orvarying, or changing or varying slightly again so that some reasonableamount of variation is contemplated without departing from the spirit ofthe invention. Further, terms such as “first,” “second,” and the likeare used to describe various elements, regions, sections, etc., and arealso not intended to be limiting. Like terms refer to like elementsthroughout the description.

Spatially relative terms such as “under,” “below,” “lower,” “over,”“upper,” and the like are used for ease of description to explain thepositioning of one element relative to a second element. These terms areintended to encompass different orientations of the device in additionto different orientations than those depicted in the figures. Further,terms such as “first,” “second,” and the like are also used to describevarious elements, regions, sections, etc. and are also not intended tobe limiting. Like terms refer to like elements throughout thedescription.

As used herein, the terms “having,” “containing,” “including,”“comprising,” and the like are open ended terms that indicate thepresence of stated elements or features, but do not preclude additionalelements or features. The articles “a,” “an,” and “the” are intended toinclude the plural as well as the singular, unless the context clearlyindicates otherwise.

It is to be understood that the features of the various embodimentsdescribed herein may be combined with each other, unless specificallynoted otherwise.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

What is claimed is:
 1. An RF amplifier package, comprising: a bodysection comprising: an electrically insulating upper surface havingfirst and second opposing edge sides; and an electrically conductive diepad vertically recessed beneath the upper surface and comprising firstand second opposing sides and a third side that intersects the first andsecond sides; first and second electrically conductive leads disposed onthe upper surface, wherein the second lead extends from adjacent to thesecond side to the second edge side; and a first electrically conductivebiasing strip connected to the second lead and disposed on the uppersurface adjacent to the third side of the die pad.
 2. The RF amplifierpackage of claim 1, wherein the first biasing strip is further disposedon the upper surface adjacent to an intersection between the second andthird sides of the die pad.
 3. The RF amplifier package of claim 2,wherein: the first biasing strip comprises a first section that isconnected to the second lead and extends along a portion of the secondside, and a second elongated section that extends along the third side;and the first section and the second elongated section form an angledintersection adjacent to the intersection between the second and thirdsides.
 4. The RF amplifier package of claim 3, wherein: the second andthird sides of the die pad are substantially linear; the intersection ofthe second and third sides is substantially perpendicular; and theangled intersection between the first section and the second elongatedsection is substantially perpendicular.
 5. The RF amplifier package ofclaim 1, wherein the second elongated section extends completely alongthe third side and further to the first edge side.
 6. The RF amplifierpackage of claim 1, wherein: the die pad further comprises a fourth sidethat opposes the third side and intersects with the first and secondsides; and the RF amplifier package further comprises a secondelectrically conductive biasing strip connected to the second lead anddisposed on the upper surface adjacent to the fourth side.
 7. A packagedRF amplifier, comprising: the RF amplifier package of claim 1; and an RFtransistor mounted on the die pad, the RF transistor comprising: acontrol terminal that is electrically coupled to the first lead, areference potential terminal that directly faces and is electricallyconnected to the die pad, and an output terminal that is electricallyconnected to the second lead.
 8. The packaged RF amplifier of claim 7,further comprising a capacitor mounted on the die pad, the capacitorcomprising a first terminal that directly faces and is electricallyconnected to the die pad and a second terminal that is electricallyconnected to the first biasing strip.
 9. The packaged RF amplifier ofclaim 8, further comprising: a first set of electrically conductive bondwires, wherein each bond wire of the first set extends directly from theoutput terminal of the RF transistor to the second lead; and a secondset of electrically conductive bond wires, wherein each of the bondwires in the second set extends directly from the second terminal of thecapacitor to the first biasing strip.
 10. The packaged RF amplifier ofclaim 7, further comprising one or more passive electrical componentsdisposed on the upper surface, wherein: the first biasing stripcomprises a first section that is connected to the second lead andextends along a portion of the second side, and a second elongatedsection that extends along the third side; and the one or more passiveelectrical components are electrically connected to at least one of thefirst section and the second elongated section.
 11. An RF amplifierpackage, comprising: a body section comprising: an electricallyinsulating upper surface comprising first and second opposing edge sidesand a window frame disposed between the first and second edge sides; andan electrically conductive die pad vertically recessed beneath the uppersurface such that the die pad is exposed by the window frame; acontinuous, electrically conductive structure disposed on the uppersurface and comprising: a lead portion disposed along a first portion ofthe window frame adjacent to the die pad; and a biasing portion disposedalong a second portion of the window frame adjacent to the die pad. 12.The RF amplifier package of claim 11, wherein the biasing portionextends from adjacent to the die pad towards the first edge side. 13.The RF amplifier package of claim 11, wherein the lead portion extendsfrom adjacent to the die pad towards the second edge side.
 14. The RFamplifier package of claim 11, wherein: the die pad is rectangular; thesecond portion of the window frame comprises third and fourth opposingsides; and the biasing portion comprises a second elongated sectiondisposed along the third side and a fourth elongated section disposedalong the fourth side.
 15. The RF amplifier package of claim 14,wherein: the window frame also includes a second side comprising firstand second end sections that respectively intersect the third and fourthopposing sides; the second portion of the window frame further comprisesthe first and second end sections and the respective intersections ofthe first and second end sections with the third and fourth opposingsides.
 16. A packaged RF amplifier, comprising: the RF amplifier packageof claim 11, wherein the lead portion comprises a first lead and asecond lead; and an RF transistor mounted on the die pad, the RFtransistor comprising: a control terminal that is electrically coupledto the first lead, a reference potential terminal that directly facesand is electrically connected to the die pad, and an output terminalthat is electrically connected to the second lead.
 17. The packaged RFamplifier of claim 16, wherein the biasing portion extends from adjacentto the die pad towards the first edge side, and the lead portion extendsfrom adjacent to the die pad towards the second edge side.
 18. Thepackaged RF amplifier of claim 16, further comprising a capacitormounted on the die pad, the capacitor comprising a first terminal thatdirectly faces and is electrically connected to the die pad and a secondterminal that is electrically connected to the biasing portion.
 19. Thepackaged RF amplifier of claim 18, further comprising: a first set ofelectrically conductive bond wires, wherein each bond wire of the firstset extends directly from the output terminal of the RF transistor to anoutput lead of the RF amplifier package; and a second set ofelectrically conductive bond wires, wherein each of the bond wires inthe second set extends directly from the second terminal of thecapacitor to the biasing portion.
 20. The packaged RF amplifier of claim16, further comprising one or more passive electrical componentsdisposed on the upper surface, wherein the one or more passiveelectrical component are electrically connected to at least one of thefollowing comprising the biasing portion: a first section and a secondelongated section.